It's an important question because there will be no credible response by President Trump to Russia influencing the US democratic process via hacking if he refuses to accept it happened.

As the economist John Maynard Keynes is reported to have said, “When my information changes, I change my mind. What do you do?”

While the best available evidence points to Russian attempts to influence the US election, Trump steadfastly refuses to accept it, reportedly believing that to do so would undermine the validity of his election.

Various US intelligence agencies including the CIA and the FBI, as well as private sector security researchers, claim that Russia was behind the hacking of the Democratic Party and the release of information damaging to candidate Hillary Clinton. They further allege that the Russians were aiming to help Trump win the election as the Republican party was also reportedly hacked, but information not released.

Trump has been highly critical of the US intelligence community, saying that one of the things he knows about cyber-security is that attribution “is impossible” and that all computers are insecure.

While he may be right on computer security, strictly speaking, attribution is not impossible, just very difficult. Seeking to trace the source of a cyber-attack on a corporate network is a costly exercise which may turn out to be pointless because it does nothing to address the security issues that made you vulnerable in the first place.

However, when talking about nation-state on nation-state attacks, attribution does make a difference. And when you have the resources of 17 intelligence agencies to draw on, with access to servers and routers globally, not to mention a forensics team par excellence, attribution becomes more of a science.

Trump has every right to be sceptical, especially when it's the credibility of his mandate that hangs in the balance, but the issue is bigger than Trump – it's about the credibility of democracy.

While Trump stands firm in his assertions that he knows things that the rest of us don't – evidence which he failed to reveal as promised on either Tuesday or Wednesday – we have the right to ask, what exactly would it take to convince him?

The human condition is to live in a world where knowledge is not perfect. That's why we have the scientific method which basically says that to build knowledge, we formulate a theory, develop predictable tests, observe the results, refine the theory and repeat.

We use the best available evidence to formulate our theories and most scientific arguments boil down to a debate about the quality of the evidence.

You can argue against one dataset but your argument really only holds water if you can provide competing evidence that would tend to undermine it. In the absence of that, you run the risk of appearing pigheaded.

To support his case, Trump says that the intelligence agencies are guilty of getting it wrong in the past. True, the evidence for weapons of mass destruction (WMDs) prior to the invasion of Iraq turned out to be wrong – but that ignores the intense political pressure that the agencies were under from the administration of President Bush and the mischaracterisation of that evidence by politicians hellbent on war.

And while not a glorious episode in the history of the intelligence agencies – both in the US and the UK – it's not a sound basis for condemning all of their work.

To put it in a legal context, the US intelligence agencies have assembled a prima facie case against the Russians for hacking the Democratic Party, seeking to influence the election through the use of propaganda on social media and leaking private email correspondence.

President-elect Trump has seen the inside of enough courtrooms to know that if this case were ever to go to trial, the Russians would quite likely lose – potentially undermining the credibility of his electoral win.

The best available evidence suggests that Trump wants to avoid further erosion of his electoral mandate even if that means turning a blind eye to inconvenient ‘truths', but to deliver on his mandate to safeguard democracy he's going to need clear 20:20 vision – even if he doesn't like what he sees.

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